Inductor



oct. 5, 1943. J Q BEARD 2,331,101

INDUCTOR Filed DSC. 26 1941 Simentor Cttorneg Patented Oer. s, 1943 rNnUc'roa Joseph G. Beard, Haddonileld, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 26, 1941, Serial No. 424,533

6 Claims.

This invention relates to improvements in inductors, and particularly to a radio frequency inductor wound with a combination of stranded and solid wire conductors to obtain a predetermined ratio of reactance to resistance throughout the operating frequency range.

The ratio of the reactance to the effective resistance of a radio frequency inductor is known as the Q of the inductor. The Q of an inductor is its figure of merit, i. e., the higher the Q the greater will be the resonance rise in the resonant circuit including the coil. In inductors of the prior art type the Q usually varies widely at the diiferent frequencies, whereby the gain varies with frequency or the Q may be unduly low.

While it is desirable to have a high gain circuit, it is often desirable to have a gain which is constant, or at least does not vary too rapidly, throughout the operable frequency range. In some prior art devices, constant gain is obtained by using compound coupling, by using loss methods, or by using mechanically variable coupling.

One of the objects of the instant invention is to provide an improved inductor with means for compensating for variations of its reactance to resistance ratio in the operable frequency range. Another object is to provide an improved inductor in which a. cable of separately insulated conductors (usually called Litzendraht) and a solid wire conductor are used to provide compensation throughout the operable frequency range. An additional object is to provide means for compensating for the variation of the ratio of reactance to resistance as a function of frequency by using a combination of solid wire and Litzendraht.

The invention will be described by referring to the accompanying drawing, in which Figs. 1, 2 and 3 are circuit diagrams in which the inductors are constructed according to the invention, and Fig. 4 is a graph illustrating the difference in characteristics of Litzendraht and solid wire. Similar reference characters indicate similar elements.

Referring to Fig. 4, the lower curve I, marked solid wire, shows the Q or reactance to resistance characteristic, with respect to frequency, of an inductor wound with solid wire and resonated over the frequency range with a capacitor having the appropriate reactance. The curve l, marked Litzendraht," represents the corresponding characteristic for an inductor wound with Litzendraht. The intermediate curve 5 represents the characteristics of an inductor wound with both solid and Litzendraht conductors. It will be 0bserved that the combined winding has a Q intermediate the values of the other curves i, 3. The rate of change of Q of the Litzendraht inductor is compensated by the rate of change of Q of the solid wire inductor at frequencies lower than 1100 kilocycles per second. At higher frequencies the decreasing rate of change of Q characteristic of the Litzendraht winding is offset by the increasing rate of change of Q of the solid wire winding. The graph shows clearly that the inductor composed of the combined windings has aV Q of which the rate of change is more uniform than the rate of change of the Q of the inductor wound only with Lltzendraht, and a Q which is higher from 400 to 1100 kc. than the inductor wound only with a solid conductor.

The foregoing example, while taken from actual tests of coils of similar inductance, is not intended to represent the maximum obtainable results. It should be understood that different or the same amounts of inductance may be employed to vary the resultant characteristic. 'I'he inductors 1, 9 may be wound on separate forms and may be connected in parallel as shown in Fig. l, or may be connected in series as shown in Fig. 2. Whilethe inductors are not mutually coupled in Figs. 1 and 2, they may be mutually coupled as indicated in Fig. 3.

Thus the invention has been described as an inductor `including windings of solid and Litzendraht conductors so related that the ratio of reactance to resistance of one conductor is cornpensated by the ratio of reactance to resistance of the other conductor, whereby a more uniformly varied Q is obtained through the frequency range than would be obtained with the Litzendraht only. The inductors using the compound windingsmay be connected in series or in shunt with proper regard for the individual and algebraic sums of the inductances of the individual windings.

I claim as my invention:

l. An inductor including a winding of solid wire and a winding of Litzendraht, said windings having different ratios of reactance to resistance whereby the resultant ratio of reactance to resistance. has a predetermined value intermediate said ratios over the operable frequency range.

2. An inductor including a winding of a solid conductor, and another winding of a cable of insulated conductors, said windings having ratios of reactance to resistance which vary differently throughout the operable frequency range and having a combined ratio of reactance to resistance of a value intermediate said ratios.

ratio of the reactance to the resistance of the wire winding and a Litzendraht winding connectedin shunt, the ratio of the reactance to the resistance of the Litzendraht winding exceeding the ratio of the reactance to the resistance of the solid wire winding at the lower operating frequencies whereby the rate of variation with frequency of the Q of one winding compensates for Y the ratel of. variation with frequency of the Q Ltzendraht winding exceeding the ratio of-'the reactance to the resistance of the solid wire winding at the lower operating .frequencies'whereby the rate of variation with frequency of the Q of one winding compensates for the rate of variation with frequency of the Q of the other windin at said frequencies. f

5. A radio frequency inductor having a solid zo of theother winding atsaid frequencies.

6. A radio frequency inductor having a solid wire winding and a Litzendraht winding connected in series, the ratio of the reactance to the resistance of the Litzendraht winding exceeding ,the ratio; of the reactance to the resistance of the vsolid Wire winding at the lower operating frequencies whereby the rate of variation with frequency of the Q of one winding compensates for the rate of variation with frequency of the Q of the other winding at said frequencies.

JOSEPH G. BEARD. 

